A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
PCT patent application No. WO 99/34257 discloses a transport mechanism for transporting the substrate in a horizontal (XY) plane relative to a remainder of the apparatus.
High stiffness and small size of such transport mechanisms are characteristic parameters for use in a lithographic apparatus. The size may be limited by the space available in the apparatus. The stiffness determines the maximum acceleration that may be used, in view of distortion and resonances, and thereby influences the throughput of the apparatus. To get a high throughput, a high stiffness is desirable. The stiffness of the transport mechanism depends, at least on part, on the stiffness of the beam, which in turn depends on the elasticity of the beam and its moment of inertia. The beam is often made of almost inelastic ceramic material to achieve a high stiffness. Use of ceramic material makes the transport mechanism expensive. Moreover, even when an almost inelastic material is used, there is still a need to achieve higher stiffness.
A further problem with this type of transport mechanism is that it is typically manufactured to very high tolerances. Deformations may cause the slide to jam on the beam.